Nematogenic material which exhibit the kerr effect at isotropic temperatures

ABSTRACT

WHEREIN R is n-butyl, n-pentyl, n-hexyl, N-HEPTYL OR N-OCTYL, OR MIXTURES THEREOF OR MIXTURES OF THESE COMPOUNDS WITH OTHER NEMATOGENIC SUBSTANCES.   WHEREIN R is ethyl, n-propyl, n-butyl, n-pentyl, N-HEXYL, ISOHEXYL, N-HEPTYL OR N-OCTYL OR COMPOUNDS OF THE GENERAL FORMULA   An electro-optical light-modulation cell having a dielectric disposed between electrodes and being comprised of a nematogenic fluid in the isotropic state, is described. Said dielectric, upon application of a voltage to the electrodes, becomes double refracting. More particularly the nematogenic fluid comprises compounds of the general formula

Unite States atent OTHER PUBLICATIONS Usoltseva et al.; ChemicalCharacteristics, Structure, and Properties of Liquid Crystal, RussianChemical Reviews, Vol. 32, pp. 49550'7, Sept. 1963.

Primary ExaminerEdward S. Bauer 7 Attorney, Agent, or FirmSamuel L.Welt; Bernard S.

Leon; William G. lsgro 4 Boiler et al. Mar. 5, 1974 NEMATOGENIC MATERIALWHICH [57] ABSTRACT EXHIBIT THE KERR EFFECT AT An electro-opticallight-modulation cell having a di- ISOTROPIC TEMPERATURES electricdisposed between electrodes and being com- [75] Inventors: ArthurBoller, Binningen; Hanspeter prised of a nem1tgeI1iC fluid in theisotropic State, is

Sch rre Th il, b h f described. Said dielectric, upon application of avolts i l d age to the electrodes, becomes double refractihg. Moreparticularly the nematogenic fluid comprises 173] Asslgnee: gf n' RocheNutley compounds of the general formula [22] Filed: July 11, 1972 [2!]Appl. No.: 270,789 I [30] Foreign Application Priority Data June 21,1972 Great Britain ..28987/72 [52] US. Cl. 350/150, 252/408, 350/160 LC,wherein R is hyl, n-propyl, n-butyl, n-pentyl,

260/465 E, 260/465 D n-hexyl, isohexyl, n-heptyl or n-octyl [51] Int.Cl. G02f 1/16 or compounds of the general formula [58] Field of Search350/150, 160 LC; 252/408 [56] References Cited UNITED STATES PATENTS Q-Q H 3,687,515 8/1972 Haas et al 350/150 3,694,053 9/1972 Kahn 350/1503,499,702 3/1970 Saldmacher et al. 350/150 wherein R is nbutyl,n-pentyl, n-hexyl,

n-heptyl or n-octyl, or mixtures thereof or mixtures of these compoundswith other nematogenic substances.

17 Claims, 1 Drawing Figure NEMATOGENIC MATERIAL WHICH EXHIBIT THE KERREFFECT AT ISOTROPIC TEMPERATURES The invention relates to anelectro-optical lightmodulation cell, including a dielectric which isdisposed between electrodes and which, being comprised of a nematogenicfluid in the isotropic state, upon application of a voltage to theelectrodes, becomes doubly refracting as a result of the electro-opticalKerr effect. The negatogenic fluid used comprises compounds of formula Iand/or 11 and/or mixtures with other nematogenic substances.

Detailed Description of the Invention Light modulation cells or Kerrcells are known and until now nitrobenzene, because of its high Kerrconstant, has been the only substance used as the dielectric.

However, Kerr cells having a nitrobenzene dielectric have thedisadvantage of requiring operating voltages of several kilovolts.Operation of such a cell places exacting requirements on the rise timesand the highvoltage breakdown strength of an associated electroniccontrol system. Consequently, when the cells are intensively modulated,it is impossible to make use of the theoretically very short responsetime of nitrobenzene. A further disadvantage of Kerr cells having anitrobenzene dielectric comprises the fact that they need to berelatively thick in the direction of the light beam. For example, thethickness of the dielectric parallel to the light beam must be 5 cm. inorder to produce a phase difference of 8 0.835 A (A 583 ,um, T 24 C.) ata field strength of 24 kV cm". Cells of this thickness are unsuitablefor a number of practical applications.

The present invention provides an electro-optical light-modulation cellwhich is very quickly responsive and one requiring a control voltage ina range which only necessitates the utilization of relativelyinexpensive circuitry, using transistors where possible.

In particular, the present invention relates to an electroopticallight-modulation cell having a dielectric disposed between electrodeswhich becomes doubly refracting upon an application of a voltage to theelectrodes, in which the general formula 1 and/or 11, and/or mixtureswith other nematogenic substances.

Preferably, the nematogenic fluid compound of the above mentionedcompounds is at a temperature near the temperature T,. of the phasechange between the isotropic and the anisotropic state.

In order that the invention may be readily understood, an embodimentthereof will now be described in more detail, by way of example, withreference to the accompanying drawing. The drawing shows alightmodulation arrangement including a light-modulation cell embodyingthe invention.

As shown in the drawing, a light-modulation cell 10 comprises twoparallel rectangular electrodes 16 and 17 between which is disposed of adielectric 13 composed of a nematogenic substance. The electrodes aremade of stainless steel, but can be made of any other metal, which doesnot react with nematogenic substances, for example, gold or the like.

The distance between the electrodes depends on the diameter of a lightbeam which is to be modulated. In the example, this distance is so smallthat the nematogenic substance is held between the electrodes bycapillary forces. In such a case, no additional walls are needed forlaterally binding the space between the electrodes. If the distancebetween the electrodes is greater, the space for the dielectric must besealed on all sides, using plates of suitable size and made ofelectrically insulating material. At least two opposite insulatingplates must be transparent to the light beam, i.e., they shouldadvantageously be made of glass, acrylic glass or the like.

The dielectric is made of a nematogenic substance, i.e., a substancehaving a nematic liquid-crystal phase over a certain temperature range.Specially good results are obtained with nematogenic substances whichare dielectrically and optically strongly anisotropic and which have apronounced electric dipole moment extending parallel to the direction ofmaximum polarizability of the molecules. The substances must also have amarked tendency for parallel orientation over a number of molecularspacings, i.e., the tendency to form clusters. Since the tendency toform clusters is particularly marked in the immediate neighborhood ofthe temperature T, at which there is a change from the isotropic to thenematic state, the cell is desirably operated in the temperature range Tt s T +l C.

Particularly preferred are mixtures ofp-[(p-nhexylbenzylidene)aminolbenzonitrile andp-[(p-nbutylbenzylidene)amino]-benzonitrile in a molar ratio Of 22 l lto 1:2;

a mixture of p-[(p-n-propylbenzylidene)amino]benzonitrile andp-[(p-n-hexylbenzylidene)amino1- benzonitrile in a molar ratio of 1:2;

a mixture of p[(p-n-heptylbenzylidene)amino]ben zonitrile and ofp-[(p-n-butylbenzy1idene)amino]- benzonitrile in a molar ratio of 2:1;

a mixture of p-[(p-n-octylbenzylidene)amino]benzonitrile andp-[(p-n-pentylbenzylidene)amino]- benzonitrile in a molar ratio of 2:1;

a mixture of p-n-heptyl benzoic acid-p'-cyanophenyl ester andp-n-butylbenzoic acid-p-cyanophenyl ester or p-n-pentylbenzoicacid-pcyanophenylester in a molar ratio of 2:];

a mixture of p-n-octylbenzoic acid-p'-cyanophenyl ester andp-n-butylbenzoic acid-p'-cyanophenyl ester or p-n-hexylbenzoicacid-p'-cyanophenyl ester in a molar ratio of 2:1; or

a mixture of p-n-hexylbenzoic acid-p'-cyanophenyl ester andp-n-butylbenzoic acid-p-cyanophenyl ester in a molar ratio of 2: 1.

Compounds of formula I can be manufactured in analogy to the followingexample:

150 mg p-toluenesulfonic acid were added to 5,9 g (0,05 Mol)p-aminobenzonitrile and 6,7 g (0,05 Mol) p-ethylbenzaldehyde in mlbenzene. The resulting mixture was heated in a nitrogen atmosphereduring 1 hour under reflux (temperature of the bath The water formed wasremoved in a water separator. The benzene condensed in the refluxcondenser was passed through a layer of 50 g aluminiumoxide and returnedinto the reaction flask. After cooling, 2 g potassiumcarbonate wereadded, the mixture was filtered and the filtrate separated from thesolvent under vacuum (bath temperature 50 C). 1 1,5 g yellow oil whichcrystallized after cooling, were obtained. The resulting product wasrecrystallized several times in iso-propanol until the melting pointremains constant and the 'gaschromatography shows no impurities. Thepure p-[(p-ethylbenzylidene)amino]-benzonitri1e melted at 76,277,0 andforms liquid crystals after cooling to 63,0-59,7. UV

(ETOH); E211 25, 800 (shoulder at 316 nm) NMR, MS, Ir and microanalysecorrespond to the structure attributed to the substance.

Compounds of formula II can be manufactured in analogy to the followingexample.

5,6g (28,5 mMol) p-n-butylbenzoyl chloride in 12 ml dry benzene wereadded to 3,1 g (26 mMol) p-hydroxybenzonitrile in 25 ml dry pyridine.The resulting mixture was stirred overnight at room-temperature and then2 hours at 60 C. After cooling the mixture was extracted with ether andthe extract washed with diluted hydrochloric acid and water. 9 g crudep-nbutylbenzoic acid-p'-cyanophenyl ester were obtained. This productwas dissolved in toluene and was submitted to chromatography using 250 gsilica gel. From the resulting pure fractions, 4 g of product wereobtained after recrystallization from hexane. Melting point 67 C. Liquidcrystals are formed at 41 ,5 C. NMR and IR correspond to the structureattributed to the substance.

The light modulating arrangement shown in the drawing comprises, inaddition to cell 10, a polarizer 12 disposed upstream of the cell and ananalyzer 14 disposed downstream of the cell. A beam of light from asource 11 travels through polarizer 12 and cell parallel to theelectrodes and strikes analyzer 14. If the polarizer 12 and analyzer 114are rotated 90 relative to one another as shown by the arrow in FIG. 1and if the dielectric of cell 10 is isotropic, the light beam does notreach the eye of an observer downsteam of the analyzer 14.

Ifa d.c. (direct current) voltage is applied to the electrodes of cell10, the dielectric 12 becomes doubly refracting, so that the linearlypolarized light from polarizer 12 is converted to elliptically polarizedlight, some of which can travel through the analyzer 14. The observertherefore notices a brightening of his field of view through theanalyzer.

Maximum brightening occurs at an optical phase difference of8 =(2i+I))\/2, with i= 0, l, 2 The optical phase difference is directlyproportional to the Wavelength. the thickness of the cell or dielectricparallel to the light beam, the Kerr constant and the square of theelectric field strength.

An important criterion of the capacity of electroopticallight-modulation cells is the attainable contrast between the lightintensity when no voltage is applied to the electrodes and the lightintensity at maximum drive. The contrast obtainable in a cell embodyingthe invention is of the order of 1:1,000, and varies with the fourthpower of the field strength.

Electro-optical light-modulation cells embodying the invention aresuitable for a number of applications. In general, they can be used forcontrolling and modulating light far beyond the acoustic frequencyrange. An important application is to electronic shutters. particularlyin cases in which large aperatures are required. In very specificapplications the double refraction may be optically induced. e.g. by thefield of high-powered light sources.

We claim:

1. In an electro-optical light-modulation cell having a dielectric whichis disposed between electrodes and which becomes doubly refracting onapplication of a voltage to the electrodes, the improvement whichcomprises a dielectric in the isotropic state comprised of a compoundcharacterized by the formula wherein R is ethyl, n-propy], n butyl,n-pentyl,

n-hexyl, isohexyl, n-heptyl or n-octyl, mixtures thereof and/or mixtureswith other nematogenie substances.

2. A cell in HCCOI'CBIUC with claim 1, wherein the nematogenic fluid isat a temperature near the temperature T,. of the phase change betweenthe isotropic and the anisotropic state.

3. A cell in accordance with claim 2, wherein the temperature I of thenematogenic fluid is in the range T,. 2 l,.+1,..

4. A cell in accordance with claim 3, wherein the dielectric comprises amixture of p[(p-n-hexylbenzylidene )amino]-benzonitrile and p-[p-nbutylbenzylidene)-amino]benzonitrile in a molar ratio of 2:1 to 1:2.

5. A cell in accordance with claim 3, wherein the dielectric comprises amixture of p-[(p-npropylbenzylidene)-amino]-benzonitrile andp'[(p-nhexylbenzylidene)amino]benzonitrile in a molar ratio of 1:2.

6. A cell in accordance with claim 3, wherein the dielectric comprises amixture of p-[(p-nheptylbenzylidene)-amino]-benzonitrile and p-[(p-nbutylbenzylidene)aminolbenzonitrile in a molar ratio of 2:1.

7. A cell in accordance with claim 3, wherein the dielectric comprises amixture of p-[(p-n-octylbenzylidene)amino]-benzonitrile andp-[(p-n-pentylbenzylidene)amino]-benzonitrile in a molar ratio of 2:1.

8. A cell in accordance with claim 3, which comprises polarizers forcontinuously modulating light transmitted through the cell, onepolarizer being disposed upstream of the cell and the other beingdisposed downstream of the cell in the direction oflight travelingthrough the cell.

9. A cell in accordance with claim 8 wherein the two polarizers arecrossed.

110. In an electrooptical light-modulation cell having a dielectricwhich is disposed between electrodes and which becomes doubly refractingon application of a voltage to the electrodes, the improvement whichcomprises a dielectric in the isotropic state comprised of a compoundcharacterized by the formula:

p'-cyanophenyl ester in a molar ratio of 2: 1.

16. A cell in accordance with claim 12, which comprises polarizers forcontinuously modulating light transmitted through the cell, onepolarizer being disposed upstream of the cell and the other beingdisposed downstream of the cell in the direction of light travelingthrough the cell.

17. A cell in accordance with claim 16 wherein the two polarizers arecrossed.

2. A cell in accordance with claim 1, wherein the nematogenic fluid isat a temperature near the temperature Tc of the phase change between theisotropic and the anisotropic state.
 3. A cell in accordance with claim2, wherein the temperature t of the nematogenic fluid is in the range Tc<t < or = tc+1*c.
 4. A cell in accordance with claim 3, wherein thedielectric comprises a mixture ofp((p-n-hexylbenzylidene)amino)-benzonitrile andp-((p-n-butylbenzylidene)-amino)benzonitrile in a molar ratio of 2:1 to1:2.
 5. A cell in accordance with claim 3, wherein the dielectriccomprises a mixture of p-((p-n-propylbenzylidene)-amino)-benzonitrileand p-((p-n-hexylbenzylidene)amino)benzonitrile in a molar ratio of 1:2.6. A cell in accordance with claim 3, wherein the dielectric comprises amixture of p-((p-n-heptylbenzylidene)-amino)-benzonitrile andp-((p-n-butylbenzylidene)amino)benzonitrile in a molar ratio of 2:1. 7.A cell in accordance with claim 3, wherein the dielectric comprises amixture of p-((p-n-octylbenzylidene)amino)-benzonitrile andp-((p-n-pentylbenzylidene)amino)-benzonitrile in a molar ratio of 2:1.8. A cell in accordance with claim 3, which comprises polarizers forcontinuously modulating light transmitted through the cell, onepolarizer being disposed upstream of the cell and the other beingdisposed downstream of the cell in the direction of light travelingthrough the cell.
 9. A cell in accordance with claim 8 wherein the twopolarizers are crossed.
 10. In an electro-optical light-modulation cellhaving a dielectric which is disposed between electrodes and whichbecomes doubly refracting on application of a voltage to the electrodes,the improvement which comprises a dielectric in the isotropic statecomprised of a compound characterized by the formula:
 11. A cell inaccordance with claim 10, wherein the nematogenic fluid is at atemperature near the temperature Tc of the phase change between theisotropic and the anisotropic state.
 12. A cell in accordance with claim11, wherein the temperature t of the nematogenic fluid is in the rangeTc <t < or = tc+1*c.
 13. A cell in accordance with claim 12, wherein thedielectric comprises a mixture of p-n-heptylbenzoic acid-p''-cyanophenylester and p-n-butylbenzoic acid-p''-cyanophenyl ester orp-n-pentylbenzoic acid-p''-cyanophenyl ester in a molar ratio of 2:1.14. A cell in accordance with claim 12, wherein the dielectric comprisesa mixture of p-n-octylbenzoic acid-p''-cyanophenyl ester andp-n-butylbenzoic acid-p''-cyanophenyl ester or p-n-hexylbenzoicacid-p''-cyanophenyl ester in a molar ratio of 2:1.
 15. A cell inaccordance with claim 12, wherein the dielectric comprises a mixture ofp-n-hexylbenzoic acid-p''-cyanophenyl ester and p-n-butylbenzoicacid-p''-cyanophenyl ester in a molar ratio of 2:1.
 16. A cell inaccordance with claim 12, which comprises polarizers for continuouslymodulating light transmitted through the cell, one polarizer beingdisposed upstream of the cell and the other being disposed downstream ofthe cell in the direction of light traveling through the cell.
 17. Acell in accordance with claim 16 wherein the two polarizers are crossed.